So this is an interesting story, apparently BEA are investigating Air France take offs at Bogotá after twice they barely made it off the ground before the runway end. 5 feet over the threshold is pretty scary...Avherald suggests they have reduced their MTOW already from BOG in response. Strange it happened twice, must have been pretty hairy in the cockpit seeing the runway end rapidly approaching. I would assume they're not doing de-rated takeoffs there so I wonder what it was.

There is also a comment on Avherald (no idea if it's true) that LH also reduced their MTOW from BOG last year after a rejected takeoff incident. Seems like they've been pushing the limits on the A340-300s there.

http://avherald.com/h?article=4a81da6e

https://www.bea.aero/en/investigation-r ... -bogota-e/

It happened twice with the same aircraft, F-GLZU.

Unless it has changed, LH flies to BOG with the A340-600.

dcajet wrote:

It happened twice with the same aircraft, F-GLZU.

Unless it has changed, LH flies to BOG with the A340-600.

It says it was the same aircraft, but over on another forum someone checked the records and on the other date it wasn't the same aircraft. So maybe it just means the aircraft type?

LH use the -300 and have been doing so as long as I've been living in Bogotá which is the last year, I flew it home at christmas. Maybe they used the -600 before.

There is another thread going wondering how will AF manage the airport with twin engine aircraft. I guess the answer is nothing in the hold, or a stop to fuel the bird at a lower altitude airport.

Aesma wrote:

There is another thread going wondering how will AF manage the airport with twin engine aircraft. I guess the answer is nothing in the hold, or a stop to fuel the bird at a lower altitude airport.

More engines don't equal better performance.

jetskipper wrote:

Aesma wrote:

There is another thread going wondering how will AF manage the airport with twin engine aircraft. I guess the answer is nothing in the hold, or a stop to fuel the bird at a lower altitude airport.

More engines don't equal better performance.

For takeoff, it absolutely does.

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

Mir wrote:

jetskipper wrote:

Aesma wrote:

There is another thread going wondering how will AF manage the airport with twin engine aircraft. I guess the answer is nothing in the hold, or a stop to fuel the bird at a lower altitude airport.

More engines don't equal better performance.

For takeoff, it absolutely does.

I'm pretty sure takeoff performance is based on total available thrust, not number of engines under wings.

However, the extra engines give you more room for recovery if one of the engine fails during or right after takeoff. You will be losing 1/4 of the thrust instead of 1/2.

Just from watching Lufty A340 depart ATL, I personally don't like how long it takes the aircraft to takeoff and gain altitude. It seems like an eternity from the naked eye.

At ATL it's probably a derated take-off.

speedbird52 : you must not look at the power of two or four engines, but at the power left when one engine quits. The aircraft must be able to take-off in that case.

5ft above threshold with all engines running means they were one engine quitting away from a catastrophe.

bzcat wrote:

Mir wrote:

jetskipper wrote:

More engines don't equal better performance.

For takeoff, it absolutely does.

I'm pretty sure takeoff performance is based on total available thrust, not number of engines under wings.

However, the extra engines give you more room for recovery if one of the engine fails during or right after takeoff. You will be losing 1/4 of the thrust instead of 1/2.

All takeoff performance planning is done on the assumption that one engine will fail and the remaining engine (or engines) will have to take the airplane into the air. Two-engine aircraft are overpowered as a result, so that makes their all-engine takeoff performance better than that of a four-engine aircraft of similar size/weight. But that's ultimately irrelevant because it's the engine-out performance that matters.

speedbird52 wrote:

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

In the example you have, no. The CFM56 that the A340 uses has a max thrust of 34,000 lbs for a total of 136,000 lbs of thrust , the GenXR has 63,800 lbs of thrust for a total of 127,600 lbs for two engines, however the most powerful GE90 model, 777-300ER, has 97,300 lbs of thrust per engine. All that is irrelevant however because those engine are on aircraft that have different Max Takeoof Weights.Takeoff performance is a ratio between weight and thrust, it doesn't matter how many engine you have, if you have a lower thrust to weight ratio your takeoff performance will be better.

jetskipper wrote:

speedbird52 wrote:

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

In the example you have, no. The CFM56 that the A340 uses has a max thrust of 34,000 lbs for a total of 136,000 lbs of thrust , the GenXR has 63,800 lbs of thrust for a total of 127,600 lbs for two engines, however the most powerful GE90 model, 777-300ER, has 97,300 lbs of thrust per engine. All that is irrelevant however because those engine are on aircraft that have different Max Takeoof Weights.Takeoff performance is a ratio between weight and thrust, it doesn't matter how many engine you have, if you have a lower thrust to weight ratio your takeoff performance will be better.

No GEnx engine operates at 63K thrust let alone a 787, no idea where you came up with that number. Here are the correct thrust ratings for a GEnx-1B powered 787.
http://www.geaviation.com/sites/default ... t-genx.pdf

N14AZ wrote:

My thoughts about this incident:
1.) BOG hasn't changed
2.) the performance of the A343 hasn't changed
3.) AF has been flying to BOG for years

So I would think these were individual mistakes by the two AF-crews. And that's something that makes me nervous... How can it be that they fly to BOG for years without any incidents and now suddenly two...

On Aviation Herald there were speculations that they might have had more tail wind than expected but still.

Seems a good summary. A bit of tailwind shouldn't make that big a difference given they're supposed to be able to get into the air with 1 engine failed. Very strange. I wonder how the climb out was as well.

jetskipper wrote:

Aesma wrote:

There is another thread going wondering how will AF manage the airport with twin engine aircraft. I guess the answer is nothing in the hold, or a stop to fuel the bird at a lower altitude airport.

More engines don't equal better performance.

Normally no, but at high altitude airports quads do have an advantage over twins. The twins tend to take a considerably bigger payload penalty.

jetskipper wrote:

speedbird52 wrote:

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

In the example you have, no. The CFM56 that the A340 uses has a max thrust of 34,000 lbs for a total of 136,000 lbs of thrust , the GenXR has 63,800 lbs of thrust for a total of 127,600 lbs for two engines, however the most powerful GE90 model, 777-300ER, has 97,300 lbs of thrust per engine. All that is irrelevant however because those engine are on aircraft that have different Max Takeoof Weights.Takeoff performance is a ratio between weight and thrust, it doesn't matter how many engine you have, if you have a lower thrust to weight ratio your takeoff performance will be better.

The 777-300ER has the 115,300lbs GE90-115B

jetskipper wrote:

, the GenXR has 63,800 lbs of thrust for a total of 127,600 lbs for two engines, however the most powerful GE90 model, 777-300ER, has 97,300 lbs of thrust per engine. All that is irrelevant however because those engine are on aircraft that have different Max Takeoof Weights.Takeoff performance is a ratio between weight and thrust, it doesn't matter how many engine you have, if you have a lower thrust to weight ratio your takeoff performance will be better.

Huh? Almost all of this is incorrect.

Most notably, you're quoting the PW4098's thrust, which no airline even uses in service anymore.
The GE90-115 puts out 115,300lb/ft.

Notably, the aircraft in question did a testflight from CDG yesterday after it disappeared from the sky for almost a week.

https://flightaware.com/live/flight/FGLZU

"Zulu Uniform" was also the very aircraft that almost stalled twice during cruiseflight in 2011 and on approach to CDG in 2012.

blackbox67 wrote:

Notably, the aircraft in question did a testflight from CDG yesterday after it disappeared from the sky for almost a week.

https://flightaware.com/live/flight/FGLZU

"Zulu Uniform" was also the very aircraft that almost stalled twice during cruiseflight in 2011 and on approach to CDG in 2012.

Stalling aircraft in flight seems to be a thing for AF pilots. Especially over the South Atlantic...

N14AZ wrote:

My thoughts about this incident:
1.) BOG hasn't changed
2.) the performance of the A343 hasn't changed
3.) AF has been flying to BOG for years

So I would think these were individual mistakes by the two AF-crews. And that's something that makes me nervous... How can it be that they fly to BOG for years without any incidents and now suddenly two...

On Aviation Herald there were speculations that they might have had more tail wind than expected but still.

Wouldn't more tailwind improve takeoff performance?

This is pretty concerning for modern time aviation. I mean this is the same airline whose pilots managed to stall a modern airliner.

77west wrote:

The 777-300ER has the 115,300lbs GE90-115B

That is sea level on an ISA day, it will not generate anywhere near that much thrust at a density height of 10,000+ ft which you can find at BOG. Needless to say takeoff performance is based upon one engine inoperative.

The low height crossing could be explained by incorrect trim position. Having the CG forward has the same effect as increasing the TOW.

QueenoftheSkies wrote:

Wouldn't more tailwind improve takeoff performance?

No. On the face of it, I can see how one would come to that conclusion. If we think of a cyclist, a tailwind helps reduce wind resistance allowing the cyclist to accelerate more quickly and maintain higher speeds. However when you consider that the important thing in getting a plane off the ground is the speed of the air passing over the wing, a tailwind goes from being a friend to an enemy. A tailwind runs in the same direction as the plane, which reduces the windspeed over the wing, therefore requiring a faster and longer take-off roll. Likewise, on landing a tailwind results in faster approach speeds which increases the stopping distance, leading to less margin of error during roll-out. Taken to the extreme, a strong tailwind during landing was one of the contributing factors of AF358. A tailwind can be manageable with normal parameters at standard airports (low elevation/not too hot) but for hot and/or high airports (like BOG or JNB), tailwinds should be avoided to the greatest extent possible.

This is why airport runway configurations can differ greatly, so as to minimize the effects of crosswinds and tailwinds. LAX's runways are all east-west since the predominant winds are going to be from the west and, to a lesser extent, the east. DEN or JFK can have winds from almost any direction, sometimes shifting several times over the course of a day, which is partially why those airports have sets of runways that run both north-south and east-west (in reality, JFK's runways are more NW-SE and NNE-SSW).

LH423

LH423 wrote:

QueenoftheSkies wrote:

Wouldn't more tailwind improve takeoff performance?

No. On the face of it, I can see how one would come to that conclusion. If we think of a cyclist, a tailwind helps reduce wind resistance allowing the cyclist to accelerate more quickly and maintain higher speeds. However when you consider that the important thing in getting a plane off the ground is the speed of the air passing over the wing, a tailwind goes from being a friend to an enemy. A tailwind runs in the same direction as the plane, which reduces the windspeed over the wing, therefore requiring a faster and longer take-off roll. Likewise, on landing a tailwind results in faster approach speeds which increases the stopping distance, leading to less margin of error during roll-out. Taken to the extreme, a strong tailwind during landing was one of the contributing factors of AF358. A tailwind can be manageable with normal parameters at standard airports (low elevation/not too hot) but for hot and/or high airports (like BOG or JNB), tailwinds should be avoided to the greatest extent possible.

This is why airport runway configurations can differ greatly, so as to minimize the effects of crosswinds and tailwinds. LAX's runways are all east-west since the predominant winds are going to be from the west and, to a lesser extent, the east. DEN or JFK can have winds from almost any direction, sometimes shifting several times over the course of a day, which is partially why those airports have sets of runways that run both north-south and east-west (in reality, JFK's runways are more NW-SE and NNE-SSW).

LH423

WOW! Thank you for that explanation, makes perfect sense now. Impressive I must say.......

CARST wrote:

blackbox67 wrote:

Notably, the aircraft in question did a testflight from CDG yesterday after it disappeared from the sky for almost a week.

https://flightaware.com/live/flight/FGLZU

"Zulu Uniform" was also the very aircraft that almost stalled twice during cruiseflight in 2011 and on approach to CDG in 2012.

Stalling aircraft in flight seems to be a thing for AF pilots. Especially over the South Atlantic...

Having just read the report as well, about the near stall in 2011 it doesn't inspire confidence http://avherald.com/h?article=44280b2a

The issue isn't the event as much as the reaction by the pilots, not realising the autopilot was disconnected for that long, really? Although it was also complete mismanagement of the weather radar that got them there in the first place. It's fair to say that had nothing to do with the specific aircraft.

Actually read an article on this a few days ago. It is not just AF, but also LH and IB who have had take-off issues at BOG with the A340s (the -600s were not mentionned as problematic). So I believe the issue is beyond an AF one. Remember the video of the B727 cargo plane unable to get necessary lift at take-off from BOG and crashing? Lengthen the runway?

speedbird52 wrote:

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

1 engine out on an A340 and you still have 75% of max thrust. 1 engine out on a 777/787/A330/A350 and you have 50% of max thrust. So yes it does make a difference on T-O.

jetskipper wrote:

speedbird52 wrote:

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

In the example you have, no. The CFM56 that the A340 uses has a max thrust of 34,000 lbs for a total of 136,000 lbs of thrust , the GenXR has 63,800 lbs of thrust for a total of 127,600 lbs for two engines, however the most powerful GE90 model, 777-300ER, has 97,300 lbs of thrust per engine. All that is irrelevant however because those engine are on aircraft that have different Max Takeoof Weights.Takeoff performance is a ratio between weight and thrust, it doesn't matter how many engine you have, if you have a lower thrust to weight ratio your takeoff performance will be better.

777-300ER& 777-200LR T-O thrust per engine is 115300 lb., The 777-300 is 98000 lb. for the lighter sorter range & 777-200ER is 93700 lb. There is not a listing for 97300 lb. for any -300ER. So the thrust for the 300ER is 230600 lb. vs 136000 lb. for A340-300 if it has the hight thrust engine, otherwise it's 124800 lb. total. At least 94600 lb. more total thrust with all engines running.

QueenoftheSkies wrote:

N14AZ wrote:

My thoughts about this incident:
1.) BOG hasn't changed
2.) the performance of the A343 hasn't changed
3.) AF has been flying to BOG for years

So I would think these were individual mistakes by the two AF-crews. And that's something that makes me nervous... How can it be that they fly to BOG for years without any incidents and now suddenly two...

On Aviation Herald there were speculations that they might have had more tail wind than expected but still.

Wouldn't more tailwind improve takeoff performance?

This is pretty concerning for modern time aviation. I mean this is the same airline whose pilots managed to stall a modern airliner.

T-O into the wind creates lift, T-O with the wind cuts lift. do no a tailwing reduces the wings ability to create lift.

rbavfan wrote:

777-300ER& 777-200LR T-O thrust per engine is 115300 lb., The 777-300 is 98000 lb. for the lighter sorter range & 777-200ER is 93700 lb. There is not a listing for 97300 lb. for any -300ER. So the thrust for the 300ER is 230600 lb. vs 136000 lb. for A340-300 if it has the hight thrust engine, otherwise it's 124800 lb. total. At least 94600 lb. more total thrust with all engines running.

None of those numbers are true for BOG due to the elevation.

On longer flights the A340-300 would lift more traffic load out of BOG than a 77W. Same applies in JNB. The key phrase in that sentence is traffic load.

Is this issue not the reason why KLM departs Quito for Amsterdam via a quick pit stop on the coast at Guayaquil to take on fuel that it can't load higher up? Maybe AF should take note.

I think it is the other way round - twins climb MUCH faster than quads in normal operation, because legally they have to have over 100% excess thrust (so if one engine goes down, they can still climb away safely), whereas a quad only needs over 33% excess thrust (so if one engine goes down, they can still climb away safely). The reason why twins lose out in hot and high in payload terms is because of the excessive thrust requirement for engine out performance and the thrust deterioration at altitude.
You only need to go and sit a mile from the end of any runway to see this, offset to one side - the quads are much lower than the twins (the worst was Concorde, which was also on the wrong side of the drag-curve and really inched into the sky - the sound was fantastic, though)

AVFCdownunder wrote:

Is this issue not the reason why KLM departs Quito for Amsterdam via a quick pit stop on the coast at Guayaquil to take on fuel that it can't load higher up? Maybe AF should take note.

KLM are using a twin, the 777 would take a huge payload hit to depart Quito for AMS. The quads don't suffer in the same way, hence was LH and IB are also using them at BOG. Which is one reason KLM also do such a route in Colombia, while other european carriers don't. See also South African, altitude at JNB is a large reason they still have a lot of quads.

It's all very bizarre if more than one airline has had this problem, if the performance calculations show you can take off safely it doesn't matter whether it's at sea level or 8,500 feet, the plane should perform as predicted. It'd be interesting to know the supposed issues LH and IB have had, as these seem to be more anecdotal than offically sourced.

Using Bogta a lot and knowing roughly where the runways end in relation to the terminals etc. I know I'd have been getting very nervous if I was on one of thede flights looking out of the window...must have startled people living nearby too.

rbavfan wrote:

speedbird52 wrote:

Maybe my knowledge is incorrect, but I am under the impression that two genxs are as or more powerful then 4 cfm56s?

1 engine out on an A340 and you still have 75% of max thrust. 1 engine out on a 777/787/A330/A350 and you have 50% of max thrust. So yes it does make a difference on T-O.

Simple math would tell you otherwise. A twin needs 100% of required engine out thrust available on only one engine. A quad needs that same 100% on three engines. This would mean that with all engines running a twin would have at least 200% of the required thrust where a quad could have anywhere as low as 133% which is a huge difference.

Planetalk wrote:

AVFCdownunder wrote:

Is this issue not the reason why KLM departs Quito for Amsterdam via a quick pit stop on the coast at Guayaquil to take on fuel that it can't load higher up? Maybe AF should take note.

KLM are using a twin, the 777 would take a huge payload hit to depart Quito for AMS. The quads don't suffer in the same way, hence was LH and IB are also using them at BOG. Which is one reason KLM also do such a route in Colombia, while other european carriers don't. See also South African, altitude at JNB is a large reason they still have a lot of quads.

It's all very bizarre if more than one airline has had this problem, if the performance calculations show you can take off safely it doesn't matter whether it's at sea level or 8,500 feet, the plane should perform as predicted. It'd be interesting to know the supposed issues LH and IB have had, as these seem to be more anecdotal than offically sourced.

Using Bogta a lot and knowing roughly where the runways end in relation to the terminals etc. I know I'd have been getting very nervous if I was on one of thede flights looking out of the window...must have startled people living nearby too.

It sounds to me that either they didn't configure the plane correctly for a safe takeoff or they didnt do the profromance calculations right. Either way a very scary thing.

Over 12,000 feet of runway to use, albeit hot and high, and they could barely get it off the ground? Something is seriously WRONG.

tp1040 wrote:

Over 12,000 feet of runway to use, albeit hot and high, and they could barely get it off the ground? Something is seriously WRONG.

Just to correct a common misconception, while high, Bogota is most certainly not hot And once the sun goes down, it's jackets and scarves time.

N14AZ wrote:

My thoughts about this incident:
1.) BOG hasn't changed
2.) the performance of the A343 hasn't changed
3.) AF has been flying to BOG for years

So I would think these were individual mistakes by the two AF-crews. And that's something that makes me nervous... How can it be that they fly to BOG for years without any incidents and now suddenly two...

Or:

4.) They've recently changed performance computations (software, method, etc.) which allows a lower thrust setting at take off.

I recall a time when my former carrier changed the max assumed temperature limit for take off from 54 Celsius to 65C. The take offs did get longer, to no one's surprise.

This looks very similar to, but still better than, the following:

Can't be as bad as this famous one.
https://youtu.be/O20fo-WqRmc

a320fan wrote:

Can't be as bad as this famous one.
https://youtu.be/O20fo-WqRmc

Got to love that Aussie sense of humour

TYCOON wrote:

Actually read an article on this a few days ago. It is not just AF, but also LH and IB who have had take-off issues at BOG with the A340s (the -600s were not mentionned as problematic). So I believe the issue is beyond an AF one. Remember the video of the B727 cargo plane unable to get necessary lift at take-off from BOG and crashing? Lengthen the runway?

Not sure because that incident did not occur in Bogotá, that happened in Puerto Carreño in rural Colombia close to the border with Venezuela. BOG also has a pretty long runway already, its 3,800 meters

AAMDanny wrote:

a320fan wrote:

Can't be as bad as this famous one.
https://youtu.be/O20fo-WqRmc

Got to love that Aussie sense of humour

I didn't even click the link but I know you must be referencing the "vodka burner" lol

zeke wrote:

77west wrote:

The 777-300ER has the 115,300lbs GE90-115B

That is sea level on an ISA day, it will not generate anywhere near that much thrust at a density height of 10,000+ ft which you can find at BOG. Needless to say takeoff performance is based upon one engine inoperative.

The low height crossing could be explained by incorrect trim position. Having the CG forward has the same effect as increasing the TOW.

I know, perhaps I should have said "is fitted with" but "has" should imply that. Of course it does not output that at BOG. The guy I quoted seemed to think the 77W was fitted with the GE90-98 or something, that's what I was correcting.

A tailwind would also have less impact at altitude, correct ? And V2 should be higher than at sea level.

Aesma wrote:

A tailwind would also have less impact at altitude, correct ? And V2 should be higher than at sea level.

To be honest I highly doubt this was a tailwind issue, Bogotá is perfectly adept at turning operations around when the wind changes, and no sensible pilot on a long haul from here would take off with and significant degree of tailwind. I quite enjoy it when they operate in the less usual direction and the planes come in close to the city and make a late turn to line up. Indeed for takeoffs the alternate direction is better because they don't go over the city.

I do know that climb gradiants are an issue for the quads and they take a different departure track to the twins - A330s and B787s to europe turn directly to destination after takeoff while the quads take a somewhat laborious detour to the southwest to gain altitude before looping back towards europe. For terrain reasons I assume. (all engines running of course). So anything slightly out of the ordinary is going to cause problems here.

AF have been making an en-route stop on the way between Bogotá and Paris quite on quite a few ocadsions of late. It has been mostly in Point a Pitre, Guadalupe; but today it's Lisbon.
Interesting to see how as AF is approaching LIS, to the north you see another A340 coming from BOG, with the same engines as the AF, even older (21 vs 18 yrs) quite happily on its way to Frankfurt non-stop.

AFAIK, quads do better from high-altitude airports because they have more turbojet vs. turbofan ratio of thrust. High bypass turbofans just don't perform as well at high altitude, somewhat obviously from the fact that the thinner air is less compressible. The turbojet section of the turbofan engines are more able to compress the air and feed it to the flame holders and turbines. Big fan turbofans...the thrust is markedly reduced.

Atlwarrior wrote:

Just from watching Lufty A340 depart ATL, I personally don't like how long it takes the aircraft to takeoff and gain altitude. It seems like an eternity from the naked eye.

You've never seen an A-7A Corsair II...

"For A-7A aircraft, high density altitude and maximum weight runway takeoffs often necessitated a "low transition", where the aircraft was intentionally held in "ground effect" a few feet off the runway during gear retraction, and as much as a 10-mile (16 km) departure at treetop altitude before reaching a safe flap retraction speed."


David

Planetalk wrote:

Aesma wrote:

A tailwind would also have less impact at altitude, correct ? And V2 should be higher than at sea level.

To be honest I highly doubt this was a tailwind issue, Bogotá is perfectly adept at turning operations around when the wind changes, and no sensible pilot on a long haul from here would take off with and significant degree of tailwind. I quite enjoy it when they operate in the less usual direction and the planes come in close to the city and make a late turn to line up. Indeed for takeoffs the alternate direction is better because they don't go over the city.

I do know that climb gradiants are an issue for the quads and they take a different departure track to the twins - A330s and B787s to europe turn directly to destination after takeoff while the quads take a somewhat laborious detour to the southwest to gain altitude before looping back towards europe. For terrain reasons I assume. (all engines running of course). So anything slightly out of the ordinary is going to cause problems here.

My limited experience at BOG is that they try to use the 13's as much as possible even if there are strong tailwinds.

rbavfan wrote:

The 777-300 is 98000 lb. for the lighter sorter range & 777-200ER is 93700 lb. There is not a listing for 97300 lb. for any -300ER.

The "98,000" is the 97,300 rounded up.... and no such engine exists anymore.

This was the PW4098, an engine that was offered on the 773A and 772ER but missed its specs by a disastrous amount, such that it only entered service with KE (all other airlines who had ordered it, rejected it prior to delivery).

KE and PW eventually worked out a deal to re-engine all of its outstanding PW4098 aircraft with PW4090s, and decommission the former.

The PW4098, along with the PW4173, is yet another of the major flops PW has had on widebody engines as of late. It was a big reason why we haven't seen Boeing/Airbus let PW anywhere near the 787/A350/777X.